1. Field of the Invention
The present invention relates to a network system, and more particularly, to a network system supporting a spanning tree protocol, a relay apparatus thereof, and a method of creating a spanning tree.
2. Description of the Related Art
An example of a network system for transmitting data between a plurality of different terminals is an Ethernet. The Ethernet utilizes a bridge or gateway as a relay apparatus for extending a network. That is, the Ethernet includes a plurality of Local Area Networks (LANs) that are connected respectively to a plurality of terminals, and a plurality of bridges which connect the LANs to one another. A message that is transmitted between the bridges can be bridged from one LAN to another LAN, for example, according to the IEEE802.ID standard which defines Media Access Control (MAC) bridging.
In such a network system which is connected by bridges, if multiple paths exist between the bridges, a loop is formed and thus a traffic looping problem occurs, in which a message sent from a bridge is circulated around the loop. In principle, only one single path has to exist between two bridges. For this reason, each bridge supports a spanning tree algorithm for executing a spanning tree protocol (referred to as a STP) based on the IEEE802.1D standard, which is used to avoid the above-mentioned traffic looping problem.
Meanwhile, it is known that the Ethernet is not suitable for transmitting multimedia data sensitive to a delay in transmission time, but recently a technique for transmitting multimedia data such as images or sounds via existing Ethernet are actively being developed. Such a technique, which is called Audio Video Bridging (AVB), is being standardized by the IEEE802.1.
According to the current consensus of the AVB standardization committee, since Quality of Service (QoS) of AVB protocols 0.1AS, 1Qat, and 0.1Qav is ensured only within an AVB cloud, all bridges should be AVB bridges in order to ensure QoS.
Here, Non-AVB bridges or AVB bridges can construct a tree topology from which redundant routes are removed by applying a spanning tree protocol thereto. The tree topology includes one or several AVB clouds which are connected via non-AVB bridges. However, the tree topology has a problem in that a network range capable of ensuring transmission quality of an AVB stream is limited to within an AVB cloud. In particular, as the number of AVB clouds included in the tree topology increases, it becomes more difficult to ensure transmission quality of a multimedia stream.